sorry d, but being polite - that's not a good idea!
first off, i wouldn't want two copies of the same game (different formats or not), unless it was free. if it was free, or at least less than double the price, i'd just go halves on the game with a friend who had the other system - or alternatively sell it. there could be security measures brought in to prevent this (DRM association with gamertags, etc) but then you're just opening a entirely new world of problems.